Light emitting module

ABSTRACT

A light emitting module comprising a light guide plate and a light source. The light guide plate has a polygonal shape with a plurality of corners in a plan view. The light guide plate has a first primary face which serves as an emission face, a second primary face opposing the first primary face, and a recessed portion in the second primary face. The light source is disposed in the recessed portion. The recessed portion has an opening on the second primary face, and a bottom face having a polygonal shape in a plan view. The light source has lateral faces along sides of the bottom face of the recessed portion. In a plan view, diagonal lines connecting opposing corners of the first primary face intersect with the sides of the bottom face of the recessed portion.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2019-120060 filed on Jun. 27, 2019, and Japanese Patent Application No.2020-064515 filed on Mar. 31, 2020, the disclosures of which are herebyincorporated by reference in their entireties.

BACKGROUND

The present disclosure relates to a light emitting module.

Light emitting modules employing light emitting elements such as lightemitting diodes are widely utilized as planar light sources, forexample, backlights for liquid crystal displays. For example, indirect-lit liquid crystal displays in which planar light sources areinstalled on the rear surfaces of the liquid crystal panels, there is anincreasing demand for thinner planar light sources. In a configurationin which the distance between the light source and the emission face ofa light guide plate is short as the planar light source becomes thinner,light is not fully diffused which tends to cause luminancenon-uniformity and color non-uniformity to occur in the emission face.See, for example, Japanese Patent Publication No. 2018-133304.

SUMMARY

One of the objects of the present disclosure is to provide a lightemitting module in which luminance non-uniformity and colornon-uniformity in the emission face of the light guide plate may bereduced.

A light emitting module according to certain embodiment of the presentdisclosure includes a light guide plate and a light source. The lightguide plate has a polygonal shape with a plurality of corners in a planview. The light guide plate has a first primary face which serves as anemission face, a second primary face opposing the first primary face,and a recessed portion in the second primary face. The light source isdisposed in the recessed portion. The recessed portion defines anopening on the second primary face, and a bottom face having a polygonalshape in a plan view. The light source has lateral faces along sides ofthe bottom face of the recessed portion. In a plan view, diagonal linesconnecting opposing corners of the first primary face intersect with thesides of the bottom face of the recessed portion.

In accordance with the present disclosure, a light emitting module inwhich luminance non-uniformity and color non-uniformity in the emissionface of the light guide plate may be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic top view of a light emitting module according toan embodiment of the present disclosure.

FIG. 2 is a sectional view taken along line A-A in FIG. 1.

FIG. 3 is a sectional view taken along line B-B in FIG. 1.

FIG. 4 is a perspective view of the elements in the recessed portion ofthe light guide plate in the light emitting module according to theembodiment.

FIG. 5 is a schematic view of the interfaces between the light guideplate and the light transmitting part in the light emitting moduleaccording to the embodiment.

FIG. 6A is a schematic sectional view showing a method of manufacturinga light emitting module according to the embodiment.

FIG. 6B is a schematic sectional view showing a method of manufacturinga light emitting module according to the embodiment.

FIG. 6C is a schematic sectional view showing a method of manufacturinga light emitting module according to the embodiment.

FIG. 7 is a schematic top view of a light emitting module according toanother embodiment of the present disclosure.

DESCRIPTION

Certain embodiments of the present disclosure will be explained belowwith reference to the accompanying drawings. In the drawings, the sameelements are denoted with the same reference numerals.

FIG. 1 is a schematic top view of a light emitting module 1 according toan embodiment of the present disclosure. FIG. 2 is a sectional viewtaken along line A-A in FIG. 1.

The light emitting module 1 includes a light guide plate 10 and a lightsource 20. The light source 20 may include a light emitting element 21,a phosphor layer 22, and a cover member 23.

The light guide plate 10 transmits the light emitted by the light source20. Examples of materials for the light guide plate 10 include athermoplastic resin such as acrylic, polycarbonate, cyclic polyolefin,polyethylene terephthalate, and polyester, a thermosetting resin such asepoxy and silicone, and glass. Among these examples, polycarbonate ispreferable due to its highly light transmissivity and inexpensiveness.

The light guide plate 10 has a first primary face 11, which serves asthe emission face, a second primary face 12 opposing the first primaryface 11, and a recessed portion 15 created in the second primary face12. Furthermore, the light guide plate 10 may have lateral faces 13contiguous with the first primary face 11, and oblique faces 14 betweenthe lateral faces 13 and the second primary face 12.

At least the phosphor layer 22 of the light source 20 may be disposed inthe recessed portion 15 of the light guide plate 10. The light emittingelement 21 may be disposed on the face of the phosphor layer 22 oppositethe face that opposes the first primary face 11 of the light guide plate10. The recessed portion 15 can function as a positioning part for thelight source 20 relative to the light guide plate 10.

The light emitting element 21 has a primary emission face 21 b andincludes a pair of positive and negative electrodes 21 a on the oppositeside of the primary emission face 21 b. The light emitting element 21has a semiconductor stack structure. The semiconductor stack structureincludes, for example, In_(x)Al_(y)Ga_(1-x-y)N (0≤x, 0≤y, x+y≤1) and canemit blue light.

The primary emission face 21 b of the light emitting element 21 may beadhered to the phosphor layer 22 using, for example, a lighttransmissive adhesive. In the example shown in FIG. 2 and FIG. 3, thelateral faces and the electrodes 21 a of the light emitting element 21are positioned outside of the recessed portion 15. Alternatively, thelight emitting element 21 may be disposed in the recessed portion 15. Acover member 23 may be disposed on the lateral faces of the lightemitting element 21. The cover member 23 may also be disposed betweenthe electrodes 21 a at the lower face of the light emitting element 21.The cover member 23 reflects the light emitted by the light emittingelement 21 and the phosphor in the phosphor layer 22. It is made of, forexample, a resin containing a white pigment or the like. Particularly,the cover member 23 is preferably formed of a silicone resin containingtitanium oxide.

The phosphor layer 22 may be made of abase material and a phosphordispersed in the base material. For example, an epoxy resin, siliconeresin, glass, or the like may be used as the base material for thephosphor layer 22. From the light resistance and formabilityperspectives, a silicone resin is preferably used for the base material.

The phosphor is excited by the light emitted from the light emittingelement 21, and emits light of a different wavelength from that of thelight emitted by the light emitting element 21. Examples of usablephosphor include YAG phosphors, LAG phosphors, β-SiAlON phosphors, CASNphosphors, KSF-based phosphors, quantum dot phosphors, and the like. Thephosphor layer 22 may contain one or more types of phosphors.

An optical function part 32 may be disposed on the first primary face 11of the light guide plate 10. The optical function part 32 may bedisposed in the position facing the recessed portion 15 formed in thesecond primary face 12. The optical axis of the light emitting element21 and the optical axis of the optical function part 32 preferablycoincide with one another. The optical function part 32 may have theshape of, for example, an inverted cone, inverted polygonal pyramid suchas inverted quadrangular or hexagonal pyramid, inverted frustum,inverted pyramidal frustum, or the like.

The optical function part 32 may comprise or be alight transmissiveresin, glass, or air layer having a lower refractive index than therefractive index of the light guide plate 10, and may function as a lensto diffuse light in the extension direction of the first surface of thelight guide plate 10 by refracting the light at the interfaces betweenthe light guide plate 10 and the optical function part 32. The lightguide plate 10 may alternatively have a configuration in which a lightreflecting material (e.g., a metal reflective film or a white resin) isdisposed in the recess having oblique faces, for example.

The recessed portion 15 may have an opening on the second primary face12, and may have a bottom face 17 located more closely to the firstprimary face 11 than the second primary face 12. A light scatteringlayer 31 containing a light scattering agent may be disposed on thebottom face 17 of the recessed portion 15. The light scattering layer 31may be disposed between the bottom face 17 of the recessed portion 15and the phosphor layer 22. The light scattering layer 31 may scatter andreturn downwards a portion of the light emitted straight up from thelight emitting element 21. Accordingly, the area and its vicinitydirectly above the light source 20 in the first primary face 11 of thelight guide plate 10, which is the emission face of the light emittingmodule 1, is less likely to be excessively brighter than the remainingarea. The light scattering layer 31 may be omitted, in which case thephosphor layer 22 may be disposed directly on the bottom face 17 of therecessed portion 15.

Alight transmitting part 60 may be disposed in the recessed portion 15and surrounding the light source (specifically, surrounding the phosphorlayer 22 and surrounding of the light scattering layer 31). The lighttransmitting part 60 may comprise or may be a light transmissive resinpart which transmits the light emitted from the light source 20. Therefractive index of the light transmissive resin part may be lower thanthe refractive index of the light guide plate 10. The second lighttransmitting part 60 may be a void or air layer.

The light guide plate 10 may have oblique faces 14 each forming anobtuse angle and contiguous with the second primary face 12. The obliquefaces 14 and the second primary face 12 may be covered with a lightreflecting resin part 40.

The light reflecting resin part 40 reflects the light emitted by thelight source 20 and is formed of, for example, a resin containing awhite pigment or the like. Particularly, the light reflecting resin part40 is preferably a silicone resin containing titanium oxide.

The electrodes 21 a of the light emitting element 21 are respectivelyconnected to the wirings 52. The light reflecting resin part 40 may bean insulator and may cover the lateral faces of the electrodes 21 a ofthe light emitting element 21.

The light reflecting resin part 40 may be joined to a wiring board 50.The wiring board 50 may have an insulating base 51, wirings 54 disposedon the rear surface of the base 51, and vias 53 penetrating the base 51.The vias 53 respectively connect the wirings 52 and the wirings 54, andthe electrodes 21 a of the light emitting element 21 are respectivelyelectrically connected to the wirings 54 through the wirings 52 and thevias 53.

Examples of materials for the base 51 of the wiring board 50 include aresin and a ceramic material. Examples of materials for the wirings 52and 54, and the vias 53 include copper.

In the description herein, a plan view refers to a plan view of thefirst primary face 11 of the light guide plate 10 as shown in FIG. 1. Insuch a plan view, the first primary face 11 has a polygonal shape withmultiple corners 11 a, for example, a quadrangular shape or a squareshape with four corners 11 a.

In a plan view, the bottom face 17 of the recessed portion 15 may alsohave a polygonal shape. For example, the bottom face 17 of the recessedportion 15 has four long sides 17 a and four short sides 17 b which areshorter than the long sides 17 a. Furthermore, the bottom face 17 mayhave a corner between a long side 17 a and a short side 17 b.

In a plan view, the phosphor layer 22 may be polygonal. The phosphorlayer 22 is, for example, quadrangular or square shaped in a plan viewand has four lateral faces 22 a. The four lateral faces 22 a may be eachalong the long sides 17 a of the bottom face 17 of the recessed portion15. In a plan view, the corners of the phosphor layer 22 may bepositioned to each face the short sides 17 b of the bottom face 17 ofthe recessed portion 15.

In a plan view, the diagonal lines connecting opposing corners 11 a ofthe first primary face 11 may intersect with the long sides 17 a of thebottom face 17 of the recessed portion 15. Position of the phosphorlayer 22 on the bottom face 17 of the recessed portion 15 may bedetermined such that the lateral faces 22 a of the phosphor layer 22 arealong the long sides 17 a of the bottom face 17 of the recessed portion15.

The light source 20 having a quadrangular or square shape in a plan viewmay be positioned so as to be rotated 45 degrees relative to thequadrangular or square-shaped first primary face 11 of the light guideplate 10, for example, to thereby allow the lateral faces 22 a of thephosphor layer 22 also serving as the lateral surfaces of the lightsource 20 (specifically, the sides of the quadrangular or square-shapedphosphor layer 22) to intersect with the diagonal lines connectingopposing corners 11 a of the first primary face 11 in a plan view. In aplan view, the corners of the light source 20 (specifically, the cornersof the phosphor layer 22) may be not positioned on the diagonal linesconnecting opposing corners 11 a of the first primary face 11, and maybe positioned so as not to oppose the corners 11 a. In a plan view, thecorners of the light source 20 (specifically, the corners of thephosphor layer 22) may be positioned in the regions segmented by thediagonal lines connecting opposing corners 11 a of the first primaryface 11.

In the phosphor layer 22, the lateral faces 22 a have larger areas thanthe corners. Thus, the luminance of the light exiting from the lateralfaces 22 a of the phosphor layer 22 tends to be higher than theluminance of the light exiting in diagonal directions.

In the quadrangular or square-shaped first primary face 11 of the lightguide plate 10, moreover, the distance between the central portion wherethe phosphor layer 22 is disposed and each corner 11 a is larger thanthe distance between the central portion and each side. Thus, the lighttends not to readily diffuse to the four corners of the first primaryface 11.

In accordance with the embodiment of the present disclosure, positioningthe phosphor layer 22 relative to the light guide plate 10 so as toallow the lateral faces 22 of the phosphor layer 22 to intersect withthe diagonal lines connecting opposing corners 11 a of the first primaryface 11 and to face the corners 11 a of the first primary face 11 canfacilitate the diffusion of the light exiting from the phosphor layer 22to the four corners of the first primary face 11 of the light guideplate 10. This may reduce luminance non-uniformity and colornon-uniformity in the first primary face 11 which is the emission faceof the light emitting module 1.

FIG. 3 is a sectional view taken along line B-B in FIG. 1. FIG. 4 is aperspective view of the constituent elements (e.g., the light scatteringlayer 31, the phosphor layer 22, and the light transmitting part 60) inthe recessed portion 15 of the light guide plate 10 in the lightemitting module 1 according to the embodiment.

The shape of the opening 16 of the recessed portion 15 is, for example,a quadrangular or square, and the shape of the opening 16 of therecessed portion 15 may differ from the shape of the bottom face 17 ofthe recessed portion 15.

The recessed portion 15 may have oblique faces 18 each being oblique to,and forming an obtuse angle with, the bottom face 17 of the recessedportion 15. The light transmitting part 60 may be in contact with theoblique faces 18 of the recessed portion 15, and may have oblique faces61 facing the oblique faces 18 of the recessed portion 15.

As shown in FIG. 2 and FIG. 4, the light transmitting part 60 has anupper face 63 in contact with the bottom face 17 of the recessed portion15 and vertical faces 62 orthogonal to the bottom face 17 of therecessed portion 15. The vertical faces 62 may be also in contact withthe light guide plate 10.

Forming the oblique faces 61 in the light transmitting part 60 canincrease the area of contact with the light guide plate 10 as comparedto the case in which only the upper face 63 and the vertical faces 62are in contact with the light guide plate 10. In other words, this canincrease the interfaces between the different materials, whereby thelight exiting from the phosphor layer 22 through the light transmittingpart 60 likely to enter into the light guide plate 10.

In the plan view in FIG. 1, the oblique faces 61 are positioned betweenthe corners 11 a of the first primary face 11 and the lateral faces 22 aof the phosphor layer 22, while facing the corners 11 a of the firstprimary face 11. Accordingly, the light from the phosphor layer 22 canbe readily diffused to the four corners of the first primary face 11 ofthe light guide plate 10 through the oblique faces 61 of the lighttransmitting part 60, thereby reducing luminance non-uniformity andcolor non-uniformity in the first primary face 11.

FIG. 5 is a schematic view of the interfaces between the light guideplate 10 and the light transmitting part 60.

The refractive index difference between the light transmitting part 60and the light guide plate 10 by virtue of the oblique faces 61 of thelight transmissive part 60 allows the light exiting from the lightsource 20 to readily advance in the directions of diffusion.Accordingly, the area and its vicinity directly above the light source20 in the first primary face 11 of the light guide plate 10 is lesslikely to be excessively brighter than the remaining area, therebyreducing luminance non-uniformity and color non-uniformity. Even in thecase where the light transmitting part 60 is configured as a void or airlayer, the refractive index difference from that of the light guideplate 10 similarly allows the light exiting from the light source 20 toreadily advance in the directions of diffusion.

FIGS. 6A to 6C are schematic sectional views showing a method ofmanufacturing the light emitting module 1 according to the embodiment.

As shown in FIG. 6A, a light guide plate 10 is provided. The light guideplate 10 may be formed by, for example, injection molding, transfermolding, thermal transfer, and the like. Forming a recessed portion 19where an optical function part 32 will be disposed and a recessedportion 15 where a phosphor layer 22 will be disposed all at once usinga mold can increase the positioning accuracy between the opticalfunction part 32 and the light emitting element 21.

As shown in FIG. 6B, for the light transmitting part 60, a lighttransmissive resin, for example, is supplied in the recessed portion 15.The light transmissive resin may be supplied in the recessed portion 15in a liquid or flowable state by using a method such as potting,printing, spraying, and the like.

After supplying the light transmitting part 50 to the recessed portion15, as shown in FIG. 6C, a light source 20 together with a lightscattering layer 31 is arranged in the recessed portion 15. The lightscattering layer 31 may be adhered to the bottom face 17 of the recessedportion 15.

The light scattering layer 31, the phosphor layer 22, and the lightemitting element 21 are supplied in the recessed portion 15 as one unitin the state of being bonded with one another. At this point, thephosphor layer 22 which is quadrangular or square-shaped in a plan viewis positioned in a self-aligned manner such that the lateral faces 22 aare along the long sides 17 a of the bottom face 17 of the recessedportion 15. Accordingly, the light emitting element 21 is alsopositioned relative to the light guide plate 10 in a self-alignedmanner. Because the area of the opening 16 of the recessed portion 15 islarger than the area of the bottom face 17, the light scattering layer31 and the phosphor layer 22 can be easily disposed in the recessedportion 15.

Subsequently, the optical function part 32 shown in FIG. 2 may beprovided in the recessed portion 19 on the first primary face 11 side ofthe light guide plate 10, and a light reflecting resin part 40 may bedisposed to cover the oblique faces 14 and the second primary face 12 ofthe light guide plate 10. A wiring board 50 may be adhered below thelight reflecting resin part 40.

In the light emitting module 1 according to the embodiment, because thelight emitting element 21 is mounted on the light guide plate 10, butnot on the wiring board 50, the distance between the light guide plate10 and the light emitting element 21 can be reduced. This can reduce thethickness of the light emitting module 1. Such a light emitting module 1can be used, for example, as a backlight for a liquid crystal display.The distance between the liquid crystal panel and the light emittingmodule 1 is short in, for example, a direct-lit liquid crystal displayin which the backlight is installed on the rear surface of the liquidcrystal panel. Therefore, the luminance and color non-uniformities inthe light emitting module 1 readily affect the luminance and colornon-uniformities of the liquid crystal display. Using such a lightemitting module 1 having reduced luminance and color non-uniformitiesaccording to the embodiment as the backlight of a direct-lit liquidcrystal display can contribute to reduction of the luminance and colornon-uniformities of the liquid crystal display.

FIG. 7 is a schematic top view of alight emitting module 100 accordingto another embodiment of the present disclosure.

The light emitting module 100 has a single light guide plate 10, and aplurality of cells 2 periodically arranged on the light guide plate 10.Each cell 2 has the same structure as that of the light emitting module1 described above.

In other words, the light guide plate 10 is provided with a plurality ofoptical function parts 32 on the first primary face 11 side and aplurality of recessed portions 15 on the second primary face 12 side. Ineach recessed portion 15, a light scattering layer 31, a light source20, and a light transmitting part 60 are disposed.

FIG. 7 is a plan view of the first primary face 11 of the light guideplate 10. In the plan view, each cell 2 is formed to have a quadrangularor square shape having four corners 2 a, for example. Each cell 2 may bearranged such that its sides are along the sides of the first primaryface 11 of the light guide plate 10. In a plan view, the long sides 17 aof the bottom face 17 of the recessed portion 15 and the lateral facesof the light sources 20 (specifically, the lateral faces 22 a of thephosphor layer 22) may respectively face the corners 2 a in each cell 2.The diagonal lines connecting opposing corners 2 a may intersect withthe long sides 17 a of the bottom face 17 of the recessed portion 15 ineach cell 2. The diagonal lines connecting opposing corners 2 a in acell 2 may intersect with the lateral faces 22 a of the phosphor layer22 in the cell 2.

Accordingly, the light exiting from the phosphor layer 22 in each cell 2can readily diffuse to the four corners of the cell 2. By inhibiting theluminance from concentrating in the center in each cell 2 across theentire first primary face 11, which is the emission face of the lightemitting module 100, the luminance non-uniformity and colornon-uniformity in the emission face of the light emitting module 100 canbe reduced.

In the foregoing, certain embodiments of the present disclosure havebeen explained with reference to specific examples. The presentdisclosure, however, is not limited to these specific examples. Allforms implementable by a person skilled in the art by suitably makingdesign changes based on any of the embodiments disclosed above also fallwithin the scope of the present invention so long as they encompass thesubject matter of the present disclosure. Furthermore, variousmodifications and alterations within the spirit of the presentdisclosure that could have been made by a person skilled in the art arealso considered as those falling within the scope of the presentdisclosure.

What is claimed is:
 1. A light emitting module comprising: a light guideplate having a polygonal shape with a plurality of corners in a planview, the light guide plate having a first primary face which serves asan emission face, a second primary face opposing the first primary face,and a recessed portion in the second primary face, a light sourcedisposed in the recessed portion, wherein the recessed portion has anopening on the second primary face, and a bottom face having a polygonalshape in a plan view, the light source has lateral faces along sides ofthe bottom face of the recessed portion, and in a plan view, diagonallines connecting opposing corners of the first primary face intersectwith the sides of the bottom face of the recessed portion.
 2. The lightemitting module according to claim 1, wherein the diagonal linesconnecting opposing corners of the first primary face intersect withlateral faces of a phosphor layer.
 3. The light emitting moduleaccording to claim 1, comprising: a plurality of cells each having aquadrangular shape and a recessed portion, each including a lightsource, the cells periodically arranged on the light guide plate, in aplan view, in each of the plurality of cells, the sides of the bottomface of the recessed portion and the lateral faces of the light sourcerespectively face corners of the cell.
 4. The light emitting moduleaccording to claim 1, wherein the recessed portion has an oblique facebeing oblique to the bottom face of the recessed portion, and forming anobtuse angle with the bottom face of the recessed portion.
 5. The lightemitting module according to claim 4 further comprising a lighttransmitting part disposed in the recessed portion and surrounding thelight source.
 6. The light emitting module according to claim 5, whereinthe light transmitting part comprises a light transmissive resin part.7. The light emitting module according to claim 6, wherein a refractiveindex of the light transmissive resin part is lower than a refractiveindex of the light guide plate.
 8. The light emitting module accordingto claim 1, wherein an area of the opening of the recessed portion islarger than an area of the bottom face of the recessed portion.
 9. Thelight emitting module according to claim 1, further comprising, anoptical function part disposed in the first primary face of the lightguide plate in a position to face the recessed portion, and having alower refractive index than a refractive index of the light guide plate.10. The light emitting module according to claim 1, wherein the lightsource includes a light emitting element and a phosphor layer adhered toa primary emission face of the light emitting element.